Engine Start Control Device and Method for a Hybrid Vehicle

ABSTRACT

An engine start control device for a hybrid vehicle equipped with an electric motor and an engine with an induction system, including a hybrid controller that performs an engine start determination to determine whether the engine should be started while the electric motor is running; an acceleration position sensor that detects an acceleration demand during the engine start determination; and a start/power generation motor that starts the engine, wherein the start/power generation motor controls the pressure in the induction system based on acceleration demand.

TECHNICAL FIELD

The present invention relates to an engine start control device for ahybrid vehicle which is equipped with a motor and an engine.

BACKGROUND

A hybrid vehicle having both a motor and an engine is powered only by amotor when the vehicle is under a small load. When the load increases,the hybrid vehicle starts the engine to provide additional drivingforce. When the hybrid vehicle shifts from running only with a motor tousing the engine as well, it is necessary to rapidly start the engine.If it takes a long time to start the engine, the driving force cannot besmoothly controlled, which deteriorates vehicle performance.

Therefore, the time required to start the engine may be reduced bycontrolling the action timing of the induction system at the time theengine starts. However, when the engine start time is shortened asdescribed above, the engine torque is applied immediately after thecomplete combustion of the engine start, which results in an enginestart shock. The driver tends to feel the engine start shock,particularly when the vehicle is accelerated slowly.

SUMMARY

In general, the present disclosure is directed to an engine startcontrol device for a hybrid vehicle which may prevent the shock that thedriver feels during slow acceleration and also provides good throttleresponse when rapid acceleration is required.

In one aspect, the present disclosure is directed to an engine startcontrol device for a hybrid vehicle equipped with an electric motor andan engine with an induction system, including a hybrid controller thatperforms an engine start determination to determine whether the engineshould be started while the electric motor is running, an accelerationposition sensor that detects an acceleration demand during the enginestart determination, and a start/power generation motor that starts theengine, wherein the start/power generation motor controls the pressurein the induction system based on acceleration demand.

In another aspect, the present disclosure is directed to a methodincluding determining whether an engine should be started while a motoris running, wherein the engine includes an induction system, detectingan acceleration demand of a driver during an engine start determination,and starting the engine after controlling the pressure in the inductionsystem based on the acceleration demand.

In yet another aspect, the present disclosure is directed to an enginestart control device for a hybrid vehicle equipped with an electricmotor and an engine, including means for performing an engine startdetermination while the electric motor is running, means for detectingacceleration demand of the driver during said engine startdetermination, and means for controlling the induction pressure of theinduction system to start the engine based on said acceleration demand.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram illustrating the structure of anembodiment of the engine start control device for a hybrid vehicle.

FIG. 1A is a schematic diagram illustrating the driveline of a hybridvehicle.

FIG. 1B is a plot showing the relationship between the components of aplanetary gear mechanism.

FIG. 1C is a plot showing the relationship between the components of aplanetary gear mechanism.

FIG. 2 is a main flowchart indicating the operation of the engine startcontrol device for a hybrid vehicle.

FIG. 3 is a flowchart of the target setting routine.

FIG. 4 is a graph indicating target gate opening TV01 of the throttlevalve versus the amount of pressure on the accelerator pedal.

FIG. 5 is a graph indicating target delay time Ta for the fuel injectionversus the amount of pressure on the accelerator pedal.

FIG. 6 is a graph indicating target delay time Tb for the fuel injectionversus the rate of the pressure on the accelerator pedal.

FIG. 7 is a time chart of the case where the amount of pressure on theaccelerator pedal is small (AP0≦AP01).

FIG. 8 is a time chart of the case where the amount of pressure on theaccelerator pedal is large (AP0>AP01).

DETAILED DESCRIPTION

The embodiments of the present invention will be described in detailbelow by referring to the drawings, but the present invention is notlimited to this embodiment.

FIG. 1 is a block diagram illustrating an embodiment of the engine startcontrol device for a hybrid vehicle. In FIG. 1, the thick solid lineindicates the route through which mechanical energy is transmitted, thedashed line indicates the electric power line, and the thin solid lineindicates the control line.

Referring to FIG. 1, a hybrid vehicle 10 includes an engine 11, aplanetary gear mechanism 12, a running/regenerative braking motor 13, astart/power generation motor 14, a reduction gear 15, a differentialarrangement 16, drive wheels 17, a first inverter 21, a second inverter22, a battery 23, a hybrid controller 31 and an engine controller 32.

The running/regenerative braking motor 13 is connected to engine 11through the planetary gear mechanism 12, which functions as a powerdivider. The running/regenerative braking motor 13 is used for driving(power running) and braking (regenerative braking) of the vehicle. Therunning/regenerative braking motor 13 is an alternator such as, forexample, a three-phase synchronized motor and three-phase inductionmotor.

Referring to FIG. 1A, the planetary gear mechanism 12 includes a sungear 12 a which is a first rotating element connected to start/powergeneration motor 14, ring gear 12 b which is a third rotating elementconnected to driving wheels 17 and a plurality of pinion gears 12 cwhich are engaged in the outer circumference of sun gear 12 a and theinner circumference of ring gear 12 b, which are concentrically placed.Planetary gear mechanism 12 rotatably supports the plurality of piniongears 12 c and has carrier 16 d which is a second rotating elementconnected to engine 11.

The running/regenerative braking motor 13 is placed in the driving forcetransmitting path which is located among ring gear 12 b, reduction gear15 and differential arrangement 16. According to the present embodiment,running/regenerative braking motor 13 is serially connected to the inputaxes of reduction gear 15 and differential arrangement 16. That is, ringgear 12 b which is the gear element connected to running/regenerativebraking motor 13 is connected to the driving force transmitting pathconnected to driving wheels 17. When running/regenerative braking motor13 and start/power generation motor 14 are driven to increase rotation,that is, when a positive torque is output during the positive rotation,or when a negative torque is outputted during the negative rotation,they function as motors and consume electric power from the batterythrough an inverter. Also, when running/regenerative braking motor 13and start/power generation motor 14 are driven to decrease rotation,that is, when a negative torque is output during the positive rotation,or when a positive torque is outputted during the negative rotation,they function as power generating machines and charge the batterythrough an inverter.

The driving force needed to run the vehicle is mainly outputted byengine 11 and motor 12. Typically, in the idling area which does nothave good engine efficiency, low-speed area and moderate to high speedand low loaded area, the vehicle is driven by motor where only motor 12is the source for driving the vehicle. When the demanded driving forceof the vehicle cannot be obtained only by the output of engine 11,electric power is supplied from battery 24 to drive motor 12 and thegenerated motor torque is added (assisted) to the engine torque. Motor12 collects the speed reduction energy by conducting the regenerativedriving when the speed of the vehicle is reduced and can charge thebattery through an inverter or can be driven as a power generatingmachine when the vehicle is running by the engine.

Next, the operation of planetary gear mechanism 12 will be described.When the number of the teeth of ring gear 12 b is Zr, that of sun gear12 a is Zs, the gear ratio of ring gear 12 b and sun gear 12 a is λ,λ=Zs/Zr. When the number of rotations of ring gear 12 b is Nr, that ofsun gear 12 a is Ns and that of carrier 16 d is Nc, the relationship ofthese numbers and gear ratio λ is formula (1) below:Nr+λNs=(1+λ)Nc  (1)

FIGS. 1B and 1C are collinear diagrams indicating the relationship amongthe numbers of rotations of each element of planetary gear mechanism 12.According to the collinear diagrams, sun gear 12 a and ring gear 12 bwhich are the elements of both sides, are connected to start/powergeneration motor 14 and running/regenerative braking motor 13respectively and carrier 16 d which is the element of the inside, isconnected to engine 11. Number of rotations Nr of the ring gear whichcorresponds to the number of rotations of the input of differentialarrangement 16, changes in accordance with the shift transmission ratioof the speed of the vehicle, reduction gear 15 and differentialarrangement 16. In a situation wherein the shift transmission ratio ofreduction gear 15 and differential arrangement 16 is maintained at aminimum such as in the case where the vehicle is running at a highspeed, the number of rotations Nr of the ring gear changes based on thespeed of the vehicle. Therefore, as shown in the collinear diagram ofFIG. 1B, by adjusting and controlling the number of rotations of sungear 12 a (number of rotations of start/power generation motor 14), itis possible to change or control the number of rotations of carrier 16d, that is, the number of rotations of the engine, with a high degree ofaccuracy. When the two gears of planetary gear mechanism 12 are fixed,Nr=Ns=Nc and they are driven at a gear ratio of 1. Therefore, when ringgear 12 b and carrier 16 d are attached by lock-up clutch 28, threerotating elements 16 a, 16 b and 16 d which constitute planetary gearmechanism 12 are integrally rotated.

The start/power generation motor 14 is connected to engine 11 throughpower the planetary gear mechanism 12. The start/power generation motor14 cranks engine 11 when the engine is started. Furthermore, after theengine is started, start/power generation motor 14 generates electricpower by using one part of the power of engine 11 that is distributed bythe planetary gear mechanism 12. The start/power generation motor 14 isalso an alternator such as, for example, a three-phase synchronizedmotor and three-phase induction motor.

When the vehicle is running at a low speed, it is powered by therunning/regenerative braking motor 13. When the pressure on theaccelerator pedal is increased by the driver and the driving forcedemand is increased, the engine 11 is started by start/power generationmotor 14 and the vehicle is powered by the engine 11 andrunning/regenerative braking motor 13. Then, by using a portion of theengine output, start/power generation motor 14 generates electric power.The driving force of engine 11 and running/regenerative braking motor 13is transmitted to driving wheels 17 through reduction gear 15 anddifferential arrangement 16.

The first inverter 21 electrically connects running/regenerative brakingmotor 13 to battery 23. When the vehicle is running, first inverter 21converts the direct current that is produced by battery 23 into analternate current and supplies this alternating current torunning/regenerative braking motor 13. Furthermore, during breaking,first inverter 21 converts the regenerative alternate current ofrunning/regenerative braking motor 13 into a direct current, which isthen used to charge battery 23. Here, when a direct current electricmotor is used as running/regenerative braking motor 13, a DC/DCconverter may be used as substitute for the inverter. Examples ofsuitable batteries 23 include various types of rechargeable batteriessuch as nickel hydride, lithium ion and lead acid, as well as a powercapacitor such as an electric double layer capacitor.

The second inverter 22 connects start/power generation motor 14 tobattery 23. When the vehicle is started, second inverter 22 converts thedirect current produced by battery 23 into an alternating current andsupplies this alternating current to start/power generation motor 14.Furthermore, when the vehicle is running, second inverter 22 convertsthe alternating current generated by start/power generation motor 14into a direct current which is then used to charge battery 23. Again, ifa direct current electric motor is used as start/power generation motor14, a DC/DC converter may be used as substitute for the inverter.

The hybrid controller 31 calculates the target driving force based onacceleration demand, which depends, for example, on the amount ofpressure on the acceleration pedal. The acceleration demand is detectedby an accelerator position sensor 41. Hybrid controller 31 controlsrunning/regenerative braking motor 13 and start/power generation motor14 through first inverter 21 and second inverter 22. Furthermore, hybridcontroller 31 is connected to engine controller 32 by a CANcommunication and controls engine 11 through engine controller 32.Moreover, hybrid controller 31 is connected to the battery 23 by acontrol line. Also, hybrid controller 31 includes an SOC detectingmeans, which detects the state of charge (SOC) of battery 23. When theSOC is low, hybrid controller 31 initiates start/power generation motor14 to start engine 11 and charges battery 23 with electric power, whichis generated by the driving force of engine 11 at start/power generationmotor 14.

The engine controller 32 receives a signal from hybrid controller 31 andcontrols the injection time and injected amount of fuel which issupplied to engine 11, as well as the amount that a throttle valve 11 ais opened. The throttle valve 11 a, which is positioned within theinduction system of the engine 11, may be opened or closed as necessaryby the hybrid controller 31 to control the air flow rate and pressurewithin the induction system, as well as the flow of an air/fuel mixtureinto the engine 11.

When transitioning from running with the motor alone to running with theengine, if it takes time to start the engine, the driving force may notbe smoothly controlled, which adversely affects driving performance.Therefore, it is preferable to shorten the time for starting the engine.However, when the engine is started, a shock may be generated, which thedriver easily detects as a jolt or a jerking movement of the vehiclepowertrain, particularly when the vehicle is accelerated slowly.

When acceleration demand is small, i.e. when the pressure on theaccelerator pedal exerted by the driver is small, the shock caused bythe engine start may be decreased by injecting fuel when a pressuredroop is detected inside the induction system. In addition, the throttlevalve 11 a may optionally be closed. Alternatively, the cranking timemay be extended instead of, or in addition to, injecting fuel. By doingso, it may be possible to decrease the shock at the time the enginestarts and smooth the acceleration.

As used herein the term pressure drop refers to a drop in the pressureover a given time interval of the gas flowing in the induction system ofthe engine of the vehicle.

On the other hand, when acceleration demand is great, i.e. the pressureon the accelerator pedal exerted by the driver is large, if the sameprocedure is applied, the acceleration response may deteriorate. Underthese conditions the throttle valve 11 a is opened and the fuel isinjected prior to the detection of a pressure drop inside the inductionsystem by starting the fuel injection earlier. This procedure mayprevent deterioration of the acceleration response.

The control logic of engine controller 32 will be more practicallydescribed below by referring to the flowchart of FIG. 2.

FIG. 2 is a flowchart describing exemplary operation of the engine startdevice for a hybrid vehicle. In step S1, after receiving the enginestart signal from hybrid controller 31, engine controller 32 moves on tostep S2 and subsequent steps.

In step S2, engine controller 32 determines whether or not the vehiclewas previously started by the engine (that is, whether or not this isthe first time the vehicle has been started by the engine). If thevehicle was not previously started by the engine, engine controller 32proceeds to step S3 and, if the vehicle was previously started by theengine, it proceeds to step S8.

In step S3, engine controller 32 re-sets timer T. In step S4, enginecontroller 32 sets the target. The content of the target setting routinewill be more practically described later. In step S5, engine controller32 starts cranking by start/power generation motor 14 through hybridcontroller 31.

In step S6, engine controller 32 determines whether or not timer Texceeds target time T1 which is set by target setting routine S4. Beforetimer T exceeds target time T1, engine controller 32 moves on to step S7and after timer T exceeds target time T1, engine controller 32 moves onto step S9.

In step S7, engine controller 32 sets the gate opening of throttle valve11 a to a position referred to herein as gate opening TV01, which is setby target setting routine S4. In step S8, engine controller 32calculates timer T. In step S9, engine controller 32 starts fuelinjection. In step S10, engine controller 32 resets the gate opening ofthrottle valve 11 a from TV01 to its normal position.

FIG. 3 is a flow chart illustrating an exemplary target setting routine.The target setting routine of FIG. 3 is described with reference to FIG.46. In step S41, engine controller 32 sets target gate opening TV01 ofthrottle valve 11 a, which will be explained in more detail below basedon the graph shown in FIG. 4.

FIG. 4 indicates target gate opening TV01 of the throttle valve versusacceleration demand—the amount of pressure on the accelerator pedal,and/or the output of the acceleration sensor and the like. When theamount of pressure on the accelerator pedal APO is the predeterminedvalue APO1 or lower, the target gate opening TV01 of the throttle valve11 a is completely opened. In this manner, when the pressure on theaccelerator pedal from the driver is small and the acceleration demandis small, the throttle valve 11 a is completely opened. Whenacceleration demand is great, i.e., the pressure on the acceleratorpedal from the driver is large, and the amount of pressure on theaccelerator pedal exceeds the predetermined value AP01, target gateopening TV01 of the throttle valve 11 a is set. The values in FIG. 4 aredetermined experimentally beforehand.

In step S42, engine controller 32 sets target delay time Ta for the fuelinjection based on the amount of pressure on the accelerator pedal. Morepractically, target delay time Ta is determined based on the graph shownin FIG. 5. FIG. 5 indicates target delay time Ta for the fuel injectionversus the amount of pressure on the accelerator pedal, which isdetermined experimentally beforehand. As may be seen from FIG. 5, as thepressure on the accelerator pedal exerted by the driver increases,target delay time Ta decreases and as the pressure on the acceleratorpedal exerted by the driver decreases, target delay time Ta increases.Especially when the amount of pressure on the accelerator pedal exertedby the driver is small, the required driving force may be small. In thiscase, for example, it is assumed that it is necessary to start engine 11since the SOC of battery 23 is small. Therefore, target delay time Ta isextended to alleviate shock at the time of the engine start.

In step S43, engine controller 32 may set target delay time Tb for thefuel injection based on the rate of the pressure on the acceleratorpedal. More practically, target delay time Tb may be determined based onthe graph shown in FIG. 6. FIG. 6 indicates target delay time Tb for thefuel injection versus the rate of the pressure on the accelerator pedal,which is determined experimentally beforehand. As may be seen from FIG.6, as the rate of the pressure on the accelerator pedal exerted by thedriver increases, target delay time Tb decreases and as the rate of thepressure on the accelerator pedal exerted by the driver decreases,target delay time Tb increases.

In step S44, engine controller 32 compares the size of target delaytimes Ta and Tb. When Ta≦Tb, engine controller 32 moves on to step S45and sets Ta as target delay time T1. When Ta>Tb, engine controller 32moves on to step S46 and sets Tb as target delay time T1.

FIG. 7 is a time chart illustrating the case where the amount ofpressure exerted by the driver on the accelerator pedal is small(AP0≦AP01). Until time t 11, the amount of pressure on the acceleratorpedal from the driver is small (FIG. 7(F)) and the vehicle runs only byrunning/regenerative braking motor 13 (FIGS. 7(E) and (G)).

At time t 11 when the amount of pressure on the accelerator pedalexerted by the driver increases (FIG. 7(F)), the torque ofrunning/regenerative braking motor 13 increases (FIG. 7(G)).

At time t 12 when the amount of pressure on the accelerator pedalexceeds standard value AP02 (FIG. 7(F)), the control shown in theflowchart of FIG. 2 is started (step S1→S2 of FIG. 2).

After timer T is re-set (step S3 of FIG. 2), the target value is set(step S4 of FIG. 2). Here, the amount of pressure on the acceleratorpedal AP0 is predetermined value AP01 or less and target gate openingTV01 of the throttle valve 11 a is completely closed. Also, target delaytime T1 is the smaller of target delay time Ta for the fuel injection,which is set based on the amount of pressure on the accelerator pedal,or target delay time Tb for the fuel injection, which is set based onthe rate of the pressure on the accelerator pedal.

Next, cranking of engine 11 is started by start/power generation motor14 (FIG. 7(A) and step S5 of FIG. 2) and the gate opening of thethrottle valve 11 a becomes TV01 (FIG. 7(B) and step S7 of FIG. 2).

Then, at time t 13 when timer T goes beyond target delay time T1 (Yes instep S6 of FIG. 2), the fuel injection is started (FIG. 7(D) and step S9of FIG. 2) and at the same time the gate opening of throttle valve 11 ais changed back from TV01 to the normal gate opening (FIG. 7(B) and stepS10 of FIG. 2). By doing so, engine 11 generates torque (FIG. 7(E)). Inthis way, throttle valve 11 a is completely closed and a pressure dropdevelops inside the induction system of the engine 11 (FIG. 7(C)).Therefore, it is possible to reduce the shock at the time of the enginestart.

FIG. 8 is a time chart indicating the case where the amount of pressureon the accelerator pedal is large (AP0>AP01). Until time t 21, theamount of pressure on the accelerator pedal exerted by the driver issmall (FIG. 8(F)), and the vehicle runs only by running/regenerativebraking motor 13 (FIGS. 8(E) and (G)).

At time t 21 when the amount of pressure on the accelerator pedalexerted by the driver is increased (FIG. 8(F)), the torque ofrunning/regenerative braking motor 13 is increased (FIG. 8(G)). At timet 22 when the amount of pressure on the accelerator pedal exceedsstandard value AP02 (FIG. 8(F)), the control logic shown in theflowchart of FIG. 2 is started (step S1→S2 of FIG. 2).

After timer T is re-set (step S3 of FIG. 2), the target value is set(step S4 of FIG. 2). Here, amount of pressure on the accelerator pedalAP0 is larger than predetermined value AP01 and target gate opening TV01is determined based on FIG. 2. Also, target delay time T1 is the smallerof target delay time Ta for the fuel injection, which is set based onthe amount of pressure on the accelerator pedal, or target delay time Tbfor the fuel injection, which is set based on the rate of the pressureon the accelerator pedal.

Next, cranking of engine 11 is started by start/power generation motor14 (FIG. 8(A) and step S5 of FIG. 2) and the gate opening of thethrottle valve 11 a is set at TV01 (FIG. 8(B) and step S7 of FIG. 2).

Then, at time t 23 when timer T goes beyond target delay time T1 (Yes instep S6 of FIG. 2), the fuel injection is started (FIG. 8(D) and step S9of FIG. 2) and at the same time the gate opening of throttle valve 11 ais changed to the normal gate opening (FIG. 8(B) and step S10 of FIG.2). By doing so, engine 11 generates torque (FIG. 8(E)). In this way,throttle valve 11 a has a gate opening of TV01 and the pressure drop isnot developed inside the induction system (FIG. 8(C)). Therefore, engine11 generates significant torque and it is possible to sufficientlyincrease speed.

The engine start control device for a hybrid vehicle that is describedabove prevents the shock that the driver feels when acceleration demandis small and the vehicle is accelerated slowly. In addition, the enginestart control device makes it possible to accelerate the vehicle with agood throttle response when acceleration demand is great and the vehicleis rapidly accelerated.

The present invention is not limited to the above described embodimentand can be changed to a variety of forms within the scope of itstechnological idea. Various embodiments of the invention have beendescribed. These and other embodiments are within the scope of thefollowing claims.

1. An engine start control device for a hybrid vehicle equipped with anelectric motor and an engine with an induction system, comprising: ahybrid controller that performs an engine start determination todetermine whether the engine should be started while the electric motoris running; an acceleration position sensor that detects an accelerationdemand during the engine start determination; and a start/powergeneration motor that starts the engine, wherein the start/powergeneration motor controls a pressure in the induction system based onacceleration demand.
 2. The engine start control device for a hybridvehicle as set forth in claim 1, wherein the hybrid controllerdetermines whether the engine should be started based on theacceleration demand of the driver.
 3. The engine start control devicefor a hybrid vehicle as set forth in claim 1, wherein the accelerationposition sensor detects the acceleration demand of the driver based onan amount of pressure on an accelerator pedal.
 4. The engine startcontrol device for a hybrid vehicle as set forth in claim 1, wherein thehybrid controller, which is equipped with a SOC detector to detect astate of battery charge, determines whether the engine should be startedbased on the state of battery charge.
 5. The engine start control devicefor a hybrid vehicle as set forth in one of claim 1, wherein thestart/power generation motor cranks the engine with a throttle valveopening based on the acceleration demand and the hybrid controllerstarts the engine by starting a fuel injection a predetermined timeafter the cranking starts.
 6. The engine start control device for ahybrid vehicle as set forth in one of claims 1, wherein the start/powergeneration motor controls the induction system pressure drop so that asthe acceleration demand decreases, the induction system pressure dropincreases.
 7. The engine start control device for a hybrid vehicle asset forth in one of claims 5, wherein the start/power generation motorencloses the throttle gate opening when the acceleration demand fallsbelow a predetermined demand.
 8. The engine start control device for ahybrid vehicle as set forth in one of claims 5, wherein the start/powergeneration motor makes the throttle gate opening as wide as theacceleration demand is large when the acceleration demand is greaterthan a predetermined demand.
 9. The engine start control device for ahybrid vehicle as set forth in one of claims 5, wherein the start/powergeneration motor extends the time from the start of the cranking to thestart of the fuel injection as the acceleration demand decreases. 10.The engine start control device for a hybrid vehicle as set forth in oneof claims 5, wherein the time from the start of the cranking to thestart of the fuel injection spent by said start/power generation motoris the lesser of the first delay time calculated based on the amount ofpressure on the accelerator pedal and the second delay time calculatedbased on the rate of the pressure on the accelerator pedal.
 11. A methodcomprising: determining whether an engine should be started while amotor is running, wherein the engine comprises an induction system;detecting an acceleration demand of a driver during an engine startdetermination; and starting the engine after controlling a pressure inthe induction system based on the acceleration demand.
 12. The method ofclaim 11, further comprising determining whether the engine should bestarted based on the acceleration demand of the driver.
 13. The methodof claim 11, wherein detecting an acceleration demand of the drivercomprises detecting the acceleration demand of the driver based on anamount of pressure on an accelerator pedal.
 14. The method of claim 11,further comprising: detecting a state of battery charge; and determiningwhether the engine should be started based on the state of batterycharge.
 15. The method of claim 11, further comprising: cranking theengine with a throttle gate opening based on the acceleration demand;and starting the engine by starting a fuel injection a predeterminedtime after the cranking starts.
 16. The method of claim 11, furthercomprising controlling the induction system pressure drop so that as theacceleration demand decreases, the induction system pressure dropincreases.
 17. The method of claim 15, further comprising enclosing thethrottle gate opening when the acceleration demand falls below apredetermined demand.
 18. The method of claim 15, further comprisingmaking the throttle gate opening as wide as the acceleration demand islarge when the acceleration demand is greater than a predetermineddemand.
 19. The method of claim 15, further comprising extending thetime from the start of the cranking to the start of the fuel injectionas the acceleration demand decreases.
 20. The method of claim 15,wherein the time from the start of the cranking to the start of the fuelinjection is the lesser of the first delay time calculated based on theamount of pressure on the accelerator pedal and the second delay timecalculated based on the rate of the pressure on the accelerator pedal.21. An engine start control device for a hybrid vehicle equipped with anelectric motor and an engine, comprising: means for performing an enginestart determination while the electric motor is running; means fordetecting an acceleration demand of a driver during the engine startdetermination; and means for controlling an induction pressure of aninduction system to start the engine based on the acceleration demand.